1. Field of the Invention
The present invention relates to a drive state control apparatus for a vehicle which can perform changeover between a two-wheel drive state and a four-wheel drive state.
2. Description of the Related Art
Conventionally, there has been widely known a transfer which includes an input shaft, a first output shaft, and a second output shaft (sac, for example, Japanese Patent No. 3050255). The input shaft is connected to an output shaft of a transmission connected to an engine of a vehicle. The first output shaft is connected to left and right rear wheels (first left and right wheels), and the second output shaft is connected to left and right front wheels (second left and right wheels).
This transfer includes a clutch mechanism which selectively establishes a “decoupled state” in which a power transmission system is formed only between the input shaft and the first output shaft, and a “coupled state” in which power transmission systems are formed between the input shaft and the first and second output shafts. This clutch mechanism is configured to be capable of adjusting maximum transmittable torque which is the maximum torque that can be transmitted in the “coupled state” the maximum drive torque that can be transmitted to the left and right front wheels).
The maximum transmittable torque is adjusted such that the greater the current for driving the clutch mechanism (an actuator within the clutch mechanism) (hereinafter referred to as “clutch drive current”), the greater the maximum transmittable torque. A state in which the maximum transmittable torque is “0” (or equal to or less than a very small value) corresponds to the “decoupled state”; and a state in which the maximum transmittable torque is greater than “0” (or the very small value) corresponds to the “coupled state.” When the clutch mechanism is in the “decoupled state.” there is established a “two-wheel drive state,” in which a power transmission system is formed only between the engine of the vehicle and the left and right rear wheels. Meanwhile, when the clutch mechanism is in the “coupled state,” there is established a “four-wheel drive state,” in which a power transmission system is formed between the engine of the vehicle and the left and right rear wheels, and another power transmission system is formed between the engine and the left and right front wheels.